Population changes of different predators during a water vole cycle in a central European mountainous habitat

Population changes in long-eared owls Asio otus, polecats Mustela putorius, red foxes Vulpes vulpes, stone martens Martes foina and badgers Meles meles were monitored during a water vole Arvicola terrestris scherman cycle in western Switzerland. Long-eared owls confirmed their status of highly mobile specialist predators in responding strongly and without time lag to water vole population changes. Even though polecats are considered generalists, they exhibited also a strong response to water vole fluctuations. Their numbers tracked water vole densities with a 1-yr time lag. Marked population changes were also recorded in red foxes and stone martens, but these changes were not related to water vole densities. Lastly, badgers did not show any significant population changes during the water vole cycle. We discuss the possible reasons for these differences and conclude that multi-factorial approach is clearly required to understand population processes in predator-prey systems.